Thread: spun bearing

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Hey guys. haven't been here for awhile but i recently rebuilt my 355 and it ran great. the only differance this time was the rods crank and cam. I just upgraded to summit stage one from stock and i put a bigger cam in. My problem is after only about 5 or so hours of running after the break in it spun a rod bearing. Now it would run around 75 psi of oil pressure at idle. A friend of mine that is a big motor head said that is way to much and starving the bottom end. Makes sence to me but how could i fix this for the next rebuild. I thought of restictors but they all say not to run with hydrolic liffters.

Too much oil pressure can push the oil through the engine so fast it doesn't take time to do any lubricating..... As for the spun bearing, what were the oil clearances on the rods??? Must have been using a high pressure oil pump when you built the engine??? For street use, I've found that a stock pump with proper clearances is usually adequate.....

It does have a high volume oil pump but it did the first time also. I cant remember the exact clerence but i usually just plastigage them. What do you think of restrictors. I figured i would run a stock pump next tme but would think the more oil to the bearings the better.

More oil is good....but too much pressure washes the bearings more then it provides lubrication.... If the oil is blowing through their with too much pressure, you will wind up with areas not getting any oil....

I'm not really the sbc guy around here, just going with what works on most engines, doubt a sbc would be any different... What the heck was your oil pressure at rpm?

Originally Posted by joe bogger

It does have a high volume oil pump but it did the first time also. I cant remember the exact clerence but i usually just plastigage them. What do you think of restrictors. I figured i would run a stock pump next tme but would think the more oil to the bearings the better.

your oil clearance i would say that could be your problem .sounds like it is set up to tight or junk could of went thru the engine for 75 psi is a bit if it your not running all out race engine all you are doing is wasting HP to drive the pump and will wear the dist cam gear off the cam . a snap a shot of the good bearings upper and lower and post it up so i can or others will tell if you have it to tight .the load side of the bearing should not be much if covers the hole half of bearing should be about 3/4 the rod can go out of round at hi rpm to for mild builds i like a bearings that is not heavily flash on it . stock feds they are a great bearing for stock use but have seen this stuff move off the bearing and build up were you do not want it and help take the bearings out bearings i use are Kings race and the oem. Speed Pro race only and clevite 77 H and Ps the ACL look good to

hay joe did you check the side clearance with new rods it may be too tight the oil gets in but cant get out fast enough might explain the high oil presure ted

Originally Posted by ted dehaan

hay joe did you check the side clearance with new rods it may be too tight the oil gets in but cant get out fast enough might explain the high oil presure ted

good point i had a set of H beams i had to reface on the old surface grinder first set out of many i never had to play with every thing needs to be check still think i would look at the oil clearance i would still think you may of over rev it pulling the rod out of round and spun it or ?? could be many things

The only engine I ever saw with 75 lbs pressure at idle had the main bearings installed top to bottom so there was no flow through them to the crankshaft. It ran a few hours and spun a rod, too. Might want to check that!

did you run a bush thru the oiling holes in the crank ?? to make sure your getting clean oil to the rods i have gone in and re work the oiling holes to were they not open up or had steel burs from drilling them some thing like not drilled all the way or junk pluging the oil flow

well i have alot to check out then. I havn't towrn it down yet. But i didn't check the side clearence or the oil holes. The machine shop was supposed to check that but thats my fault for not checking it myself. And it would run between 75 and 110 prolly. But i will have to tear it down. Thanks guys

Spun bearings have more than one possible reason:

- clearances:
Too tight will get you too little oil on the bearing and it might sieze up, too loose and the notches on the bearings aren't pressed into their proper place

- rod installed in the wrong direction:
Rods can only be built into an engine in a specific direction, because they have a chamfer on one side to accomodate the radius on the crank

- inside diameter of the rod eye
The inside diameter of the rod hole must be a bit smaller than the outside diameter of the bearing so the bearing is actually crushed a little. This prevents spinning

- oil problems
As already said: oil holes not drilled through, filled with debris, edges of the holes not deburred...

- bent rod

- crank journal out of round

- too high oil pressure won't normally spin a bearing. BUT: too high oil pressure has a cause, and that cause might also spin your bearing.

And any number of combinations of this list. Getting rods to stay put is one of the most critical and most difficult tasks on buiding an engine, specially if your using used parts. Who knows, maybe your crank journals were spun down to -.010 but you're using normal bearings? Sometimes it's the small things you don't think of...
Remember, we're talking thousandths of an inch here so use good tools for measuring...

Hope I could help,
Max